1. Field of the Invention
The present invention relates to a control device for adjusting the travelling tension and cutting position of a printing paper web in a printing apparatus which can perform printing work, folding work and cutting work in a continuous operation. More particularly, the present invention relates to a control device which can automatically control the travelling tension of the printing paper web travelling on the upstream side of a paper to fold the printing paper longitudinally and also automatically adjust the cutting position with respect to each printed pattern whenever the printing speed is changed.
2. Description of the Prior Art
One typical conventional printing apparatus such as a rotary press printing system employing a rolled type printing paper web and capable of performing a continuous operation of printing work, folding work and paper cutting work, has been commonly used in newspaper publishing. In such a rotary press printing system, a control device for automatically controlling the tension of the printing paper travelling on the upstream side of a paper former and another control device for adjusting cutting position with respect to each printed pattern are individually arranged.
The control device for the paper travelling tension has been well known as discussed in Japanese Patent Publication No. 60-38309, titled "Paper Travelling Tension Control Device in Rotary Press" (referred as 1st prior art). The control device for the paper cutting position has been well known as discussed in Japanese Patent Application Laid Open Publication No. 63-97566, titled "Paper Cutting Position Automatic Control Device in Rotary Press" (referred as 2nd prior art).
The control device shown in the 1st prior art includes a detector which detects the travelling tension of each travelling paper at the upstream side of a drag roller and outputs the detected signal as an electric signal. Further, the control device includes a comparator which compares the detected signal with a reference signal representing a control range and outputs a compared signal resulting from the comparison. According to this compared signal, a pneumatic control means generates pneumatic pressure to automatically adjust the pressure force of propeller rollers applied onto the drag roller above the drag roller and the pressure force of a movable roller of a pair of nipping rollers below the drag roller with respect to a fixed roller of the nipping roller pair. This pneumatic pressure control operation can also adjust the contacting pressure for dragging the printing paper between the fixed roller of the nipping rollers and the drag roller, and thus the paper travelling speed is controlled. The tension of the travelling paper is also maintained in a constant state.
The device shown in the 2nd prior art discloses an adjustable roller arranged in a paper travelling system. This adjustable roller can be moved to change the length from a printing device to a folding device to correct each cutting length of the printing paper with a change in the printed pattern. Further, in this prior art, a cutting mark is also printed on each printed section and a cutting cylinder is provided with an encoder. A mark detector is arranged in front of the folding device to detect the cutting mark printed on the printed section travelling immediately before the folding device. The encoder can always detect the revolving phase of the cutting cylinder as a digital signal. This digital signal is compared with the detected signal by the mark detector to calculate a phase difference between the detected signal and preset reference signal. According to this calculation, the adjustable roller is moved in response to the phase difference. In detail, the adjustable roller is moved the distance corresponding to the absolute value of the phase difference and in the direction corresponding to the plus or minus value of the phase difference. Further, another encoder is set in a transmission between the adjustable roller and its driving motor to calculate the moved distance. The driving motor is stopped whenever the calculated value is zero.
In the 1st prior art, the paper travelling tension is controlled by changing the pressure force of the propeller roller onto the drag roller above the propeller roller and the pressure force of the movable roller of the nipping roller pair onto the fixed roller of the nipping roller pair. This control is conducted as follows. The drag roller and the fixed roller of the nipping roller pair are driven at a slightly faster speed than the travelling speed of the printing paper at the upstream side of the drag roller, for example, the feeding speed of the printing paper from the printing section. Then, the travelling tension of the printing paper at the upstream side adjacent to the drag roller is detected.
When the detected tension value is greater than a reference value, the pressure force of the propeller roller is decreased to lower the contact-friction force generated between the drag roller and the printing paper and the overlapped sections of the printing papers. Further, the travelling speed of the printing paper by the drag roller is also reduced so that he travelling tension of the printing paper between the printing section and the drag roller is decreased. On the same occasion, the pressure force of the movable nipping roller is also decreased to lower the contact-friction force generated between the fixed nipping roller and the printing paper, and the overlapped sections of the printing paper. The travelling speed of the printing paper by the fixed nipping roller is also reduced to be in balance with the travelling speed of the paper by the drag roller.
On the other hand, when the detected tension value is smaller than the reference value, the pressure forces of the propeller roller and the movable nipping roller are increased to increase the travelling speed of the printing paper by the drag roller and the fixed nipping roller. Thus, the travelling tension between the printing section and the drag roller is increased and the travelling speed of the printing paper which is controlled by the drag roller is balanced with that of the fixed nipping roller.
This control system is effective when the rotary press is driven at a constant speed or when changing at a slow speed.
However, the following problems occur when the rotary press is driven to change speeds quickly, as for example at the start or end of its operation.
At the start of its operation, after receiving a start signal, the rotary press is supplied with a speed-up signal to increase its driving speed until it reaches a preset value. On the same occasion, the revolving speed of the printing cylinder of the printing section, the drag roller, the fixed nipping roller and the other driven revolving members are also increased. Many guide rollers which are not driven and which are arranged between the printing cylinder and the drag roller for guiding the printing paper through the press are revolved by a contact-friction force created between the travelling printing paper and the guide rollers. Immediately after starting the printing operation, the printing speed is quickly increased. However, the circumferential speed of the guide rollers can not follow the travelling speed of the printing paper due to the friction resistance generated around the bearings of the guide rollers. The guide rollers thus act as a load against the travelling paper. Therefore, the travelling tension applied to the printing paper between the printing section and the drag roller is not uniform. Travelling tension near the downstream side of the printing section is smaller than the travelling tension near the upstream side of the drag roller. This reduces the pressure force of the propeller roller and the pressure force of the movable nipping roller. The contact-friction forces generated between the drag roller and the travelling paper, between the fixed nipping roller and the travelling paper, and between the lapped printing papers are also decreased. Thus, the travelling speed of the printing paper is lower than when the printing operation is conducted at a constant speed. On the contrary, a cutting and folding cylinder of the folding section is driven in synchronism with the driven revolving members to ensure that the printed section coincides with the cutting interval. However, when the printed section is delayed, regardless of the revolving speed of the driven revolving members, the cut line made by the cutting and folding cylinder doe snot coincide with the actually printed section as shown in FIG. 4.
At the end of its operation, after receiving a deceleration signal, the revolving speed of the rotary press is reduced to a preset value. On the same occasion, each revolving speed of the driven revolving members are also lowered. The guide rollers are, however, free from the driven revolving members, and thus they have a tendency to revolve at a high speed owing to their own inertia force. The circumferential speed of the guide rollers cannot follow the reduction of the travelling speed of the printing paper, and the guide rollers act as a counter-force against the reduction of the travelling speed. Therefore, the printing paper is forcibly fed by the guide rollers. Thus, the travelling tension of the printing paper near the downstream side of the printing section is greater than the travelling tension near the upstream side of the drag roller where the printing paper becomes oversupplied by the feeding motion of the guide rollers. Then, the pressure force of the propeller roller and the pressure force of the movable nipping roller are increased. The contact-friction forces created by the drag roller, the fixed nipping roller, and the lapped printing papers are also increased. The paper therefore travels at a higher speed as compared to when the printing operation is conducted at a constant speed. As a result, the printed section of the printing paper is advanced beyond the line to be cut, the normal position of the cut line being shown in FIG. 3. On the contrary, the cutting and folding cylinder is driven in synchronism with the driven revolving members to synchronize the cutting timing with the paper travelling speed. Therefore, when the printed section is advanced, the line which is cut by the cutting and folding cylinder does not coincide with the actually printed section as is shown in FIG. 5.
In order to resolve this problem, the cutting position control device shown in the 2nd prior art has been provided with a capability to coincide the printed section with the cutting line. However, this control device requires a mark detecting means for detecting a cutting mark to correctly indicate the printed section location and a phase detecting means for detecting the revolving phase of the cutting and folding cylinder. These means increase the production cost of the printed matters and the printing apparatus per se. Further, this device will start its correcting operation after deviation between the printed section and the cutting position is generated. Thus, this device cannot prevent the generation of such deviation, and requires a relative long time to return the printing apparatus to its regular operational mode after the deviation is detected. Accordingly, this device cannot overcome a loss in production due to the deviation between the printed section and the cut position.